96 astro knocking

[SSAstro]

alright i havent been on in a while but i really need some help the astro finally died at 275,000 miles but with all the money i have sunk into it i dont want to junk it im pretty sure it has at least two main bearings shot. my question is has anyone had any luck with just replacing the bearings in these or my other option is a crank kit from napa. i also have considered doing a newer 4.3 swap to 03 or newer since i can readily find low mileage ones that are complete with the upgraded injectors but not sure how that would work out i know there are some differences but any input would be great